Procedures for preparing photographic images in silver by diffusion transfer principles are well known in the art. For the formation of the positive silver images, a latent image contained in an exposed photosensitive silver halide emulsion is developed and almost concurrently therewith a soluble silver complex is obtained by reaction of a silver halide solvent with unexposed and undeveloped silver halide of said emulsion. The photosensitive silver halide emulsion is developed with a processing composition which may be spread between the photosensitive element comprising the silver halide emulsion and a second element which may comprise a suitable silver precipitating layer. The processing composition effects development of the latent image in the emulsion and, substantially contemporaneous therewith, forms a soluble silver complex, for example, a thiosulfate or thiocyanate, with undeveloped silver halide. This soluble silver complex is at least in part transported in the direction of the print receiving layer and the silver thereof is precipitated in the silver precipitating element to form a positive image. Procedures of this description are disclosed, for example, in U.S. Pat. No. 2,543,181 issued to Edwin H. Land. See also Edwin H. Land, One Step Photography, Photograhic Journal, Section A, pgs. 7-15, January 1950.
Additive color reproduction may be produced by exposing a photosensitive silver halide emulsion through an additive color screen having filter media or screen elements each of an individual additive color such as red or green or blue and by viewing the reversed or positive silver image formed by transfer to a transparent print receiving element through the same or a similar screen which is suitably registered with the positive image carried in the print receiving layer. As examples of suitable film structures for employment in additive color photography, mention may be made of U.S. Pat. Nos. 2,861,885; 2,726,154; 2,944,894; 3,536,488; 3,615,426; 3,615,427; 3,615,428; 3,615,429; and 3,894,871.
U.S. Pat. No. 3,674,482, issued July 4, 1972, is directed to a silver diffusion transfer film unit which comprises a support carrying on one surface, in order, a layer containing silver precipitating nuclei, an inert non-nuclei containing protective layer and a layer containing a photosensitive silver halide emulsion. The purpose of the nonnucleated protective layer is to provide a layer over the transferred silver image after the emulsion layer has been removed subsequent to processing, which protective layer will then be the outermost layer. The material for the protective layer is one which is readily permeable to the processing composition and which will not provide sites for the nucleation of the silver forming the transferred image. A particularly preferred material employed as a protective layer comprises chitosan (deacetylated chitin).
U.S. Pat. No. 4,056,392, issued Nov. 1, 1977, is directed to a diffusion transfer film unit which comprises, in order, an additive color screen, a layer comprising silver precipitating nuclei, a layer comprising a water-soluble cupric salt and a compound selected from the group consisting of chitosan and 2-amino-2-deoxyglucose, and a photosensitive silver halide emulsion layer. By employing a water-soluble copper salt in the chitosan protective layer, an increase in D.sub.max is achieved with substantially no adverse effect on D.sub.min compared to a protective layer composed of chitosan alone.
Film units which include a support carrying a diffusion transfer image receiving layer and a photosensitive layer may be constructed to provide for the separation of the photosensitive layer from the remainder of the film unit subsequent to exposure and processing by the employment of a release layer intermediate the image-receiving layer and the photosensitive layer. Such release layers are disclosed and claimed in U.S. Pat. No. 4,366,277, issued Dec. 28, 1982, to Michael Berger and John J. Magenheimer, and copending application Ser. No. 398,669, filed July 15, 1982, of Michael Berger, Warren J. Dillman and Herbert L. Fielding (common assignee).
U.S. Pat. No. 4,366,235, issued Dec. 28, 1982 to Edwin H. Land, is directed to a method for forming a predetermined, regular geometric spaced array of sites and then forming single effective silver halide grains at said sites. Thus, by forming the sites in a predetermined spatial relationship, if the silver halide grains are formed only at the sites, each of the grains will also be located at a predetermined and substantially uniform distance from the next adjacent grain, without touching the next adjacent grain, and their geometric layout will conform to the original configuration of the sites.
U.S. Pat. No. 4,356,257, issued Oct. 26, 1982 to Arthur M. Gerber, is directed to a method for forming a photosensitive element comprising a plurality of single effective silver halide grains, which method comprises coalescing fine-grain silver halide in a plurality of predetermined, regular, geometric spaced depressions. Preferably, the coalescence is effected by contacting fine-grain silver halide with a solution of a silver halide solvent.
U.S. Pat. No. 4,353,977, issued Oct. 12, 1983 to Arthur M. Gerber, Warren D. Slafer and Vivian K. Walworth, discloses and claims a process which employs a cover sheet comprising a hydrophilic layer in contact with the relief pattern during coalescence whereby single effective grains are retained on the hydrophilic layer subsequent to separation from the relief pattern.
U.S. Pat. No. 4,362,806, issued Dec. 7, 1982 to K. E. Whitmore, is directed to photographic elements having supports providing microcells for materials such as radiation sensitive meterials including silver halide grains, imaging materials, mordants, silver precipitating agents and materials which are useful in conjunction with these materials.